Electrolysers use electricity to transform reactant chemicals to desired product chemicals through electrochemical reactions, i.e., reactions that occur at electrodes that are in contact with an electrolyte. Water electrolysers, which produce hydrogen and oxygen from water and electricity, are the most common type of electrolyser used for production of gaseous hydrogen as the main product. The most common types of commercial water electrolysers are alkaline water electrolysers (AWE) and polymer electrolyte membrane (PEM) water electrolysers.
As used herein, the terms “cell”, “electrolysis cell” and equivalent variations thereof refer to a structure comprising a cathode half cell and an anode half cell.
Also as used herein, the terms “electrolyser cell stack”, “electrolyser stack”, “stack”, or equivalent variations thereof refer to structures used for practical (commercial) electrolysers such as water electrolysers comprising multiple cells, in which the cells typically are electrically connected in series (although designs using cells connected in parallel and/or series also are known), with bipolar plates physically separating but providing electrical communication between adjacent cells. The term “electrolyser module” refers to the combination of an electrolyser stack and gas-liquid separation spaces in the same structure, which typically is of the filter press type. Further, the term “electrolyser module” as used herein may refer to an alkaline electrolyser module or a PEM electrolyser module. We previously disclosed designs for an alkaline water electrolyser module in U.S. Pat. No. 8,308,917, and for a PEM water electrolyser module in US 2011/0042228, both of which are incorporated herein by reference.
As used herein, the term “structural plate” refers to a body having a sidewall extending between opposite end faces with a half cell chamber opening, and in the case of an electrolyser module, additionally at least one degassing chamber opening extending through the structural plate between the opposite end faces. An electrolyser stack or an electrolyser module typically is constructed using a series of structural plates to define alternately cathode and anode half cell chambers, fluid flow passages, and in the case of an electrolyser module, at least one degassing chamber, and respective gas-liquid flow passages and respective degassed liquid flow passages extending between the one or more degassing chambers and the corresponding half cell chambers. The structural plates are arranged in face to face juxtaposition between opposite end pressure plates, optionally with at least one intermediate pressure plate interspersed between the structural plates along a length of the electrolyser stack or electrolyser module, to form a filter press type structure with structural plates stacked in the interior of the assembly between end pressure plates. The structural plates also hold functional components, which may include, for example, cathodes, anodes, separator membranes, current collectors, and bipolar plates, in their appropriate spatial positions and arrangement. The end pressure plates provide compression of the filter press type structure and enable pressure retention.
Generally contemplated operating pressures of electrolyser modules and electrolyser stacks lie between atmospheric pressure and 30 barg, and more typically up to 10 barg, depending on the application requirements. Older electrolyser stack designs utilize steel structural plates, which enable operation at elevated pressures, e.g., 30 barg, but present other challenges, such as very high weight, the need for electrical insulation, and potential for corrosion. Modern, “advanced” electrolyser stack and electrolyser module designs utilize structural plates made of polymeric materials, which are electrically insulating, corrosion resistant, and their light weight enables pre-assembled packaged formats, even for high output capacity units. However, typically, end pressure plates have remained essentially massive metal end flanges, even in “advanced” designs, the design approach being to control deflection, with very low stresses in the plates. This may be tolerable for smaller capacity units, but for larger capacity units, the end pressure plates become overly massive, extremely heavy, and very costly, particularly for operation at elevated pressure, since the end pressure plates must remain flat and without deflection for functionality. Welded assemblies can be added to stiffen end pressure plates and mitigate deflection, but the welded assemblies add further to weight, size, manufacturability, and especially, cost. Conventional massive end pressure plates are described in, for example, U.S. Pat. No. 8,308,917 (feature 11), US 2011/0042228 (feature 11), U.S. Pat. No. 5,139,635 (feature 12, “end flanges), U.S. Pat. No. 4,758,322 (features 404, 405, “covers”), and U.S. Pat. No. 2,075,688 (features 28, 29, “heavy end plates”).
US 2011/0024303 discloses a design utilizing a single end pressure plate, using a moving platen that is pressed against a stack of electrolyser plates, relative to a surrounding press structure that provides a fixed support so that the single moving platen can apply compressive force transversely to the stacked plates via a compression member, to compress the stacked plates between opposite faces of the surrounding press structure. Drawbacks to this design are (i) a need to design the surrounding structure for specific numbers or lengths of stacked plates; (ii) uncertainty in the amount of compressive force to apply via the compression member, e.g., for any given operating pressure and temperature, and a need to check the amount of compressive force applied under thermal and/or pressure cycling. The ability of the design to mitigate deflection of the relatively thin plates seems questionable, especially for electrolysers with a large face area operating at higher pressures. A higher degree of inherent design robustness in terms of scalability and a passive, self-regulating approach would be beneficial for practical operation.
Thus, what is needed is a simple, lightweight, cost effective, self-regulating and scalable design approach for end pressure plates for electrolyser modules and electrolyser stacks, especially large-scale electrolyser modules and electrolyser stacks that operate at higher pressures.